Shaft assembly of an exhaust-gas turbocharger

ABSTRACT

The invention relates to a shaft assembly ( 1 A) of an exhaust-gas turbocharger ( 1 ) having a shaft ( 5 ), having a turbine wheel ( 2 ) which can be connected to one end of the shaft ( 5 ) to form a rotor, haying a compressor wheel ( 12 ) which can be connected to the other end of the shaft ( 5 ), having a sealing sleeve ( 14 ) which can be located on the shaft ( 5 ) on that side of the compressor wheel ( 12 ) which faces toward the turbine wheel ( 2 ), having a shaft nut ( 15 ) which can be screwed by means of an internal thread ( 17 ) onto a free end. region ( 16 ) of the shaft ( 5 ) to fix the compressor wheel ( 12 ), wherein the shaft nut ( 15 ), in a portion ( 19 ) adjacent to the compressor wheel ( 12 ), has a turned recess ( 18 ) which adjoins the internal thread ( 17 ) and which has an inner diameter (D 2 ) greater than the internal. thread diameter (D 1 ).

The invention relates to a shaft assembly of an exhaust-gas turbochargeraccording to the preamble of claim 1.

A shaft assembly of said type according to the prior art has the problemof static overdeterminacy, which leads to bending stresses orconstraining forces in the shaft assembly. This in turn results in anundesired reduction in the elasticity of the shaft assembly, which inturn can lead to imbalances. Furthermore, in real vehicle operation, anexhaust-gas turbocharger is subjected to high accelerations andtemperatures. This leads to the occurrence of extreme forces in thescrew connection of the compressor wheel, as a result of whichretroactive settling can likewise occur.

As a result of said processes, the imbalance of the rotor or of theshaft assembly is in turn varied, which can cause undesired noises inthe vehicle.

It is therefore an object of the present invention to provide a shaftassembly of an exhaust-gas aftertreatment system according to thepreamble of claim 1, which shaft assembly permits a reduction inimbalances occurring during operation and in associated disturbingnoises.

Said object is achieved by means of the features of claim 1.

Since the shaft nut has turned recesses, the expansion length of theshaft assembly is increased, which alone contributes considerably to theachievement of the aims stated in the introduction.

The subclaims relate to advantageous refinements of the invention.

In one particularly preferred embodiment, the shaft nut has a housingregion which, by means of the enlargement of the outer diameter,provides an enlarged contact surface with the compressor wheel, whichpermits a reduced contact pressure and the realization of a greaterpreload force.

By means of turned recesses in the passage recess of the sealing sleeve,it is made possible for the sealing sleeve to tilt slightly about itscenter of gravity and to rest evenly on both sides. This yields theadvantage of the largest possible contact surface in the screwconnection and therefore a reduced contact pressure. As a result of thecentral position of the centering or of the central region between theturned recesses or the inner regions which are enlarged in terms ofinner diameter, the influence of the sealing sleeve on possibleimbalances remains unchanged.

It is preferable also for the compressor wheel to be designed to beaxially as short as possible, that is to say that part of the compressorwheel which projects axially beyond the blade leading edges is designedto be as short as possible.

In particular if aluminum alloys are used for the material of thecompressor wheel, it should be taken into consideration that thecoefficient of thermal expansion of aluminum (approximately 2.33) istwice that of steel. In this way, the stress in the shaft assembly canbe reduced by the shortening of the compressor wheel in relation toknown compressor wheels.

The shaft, or the rotor constructed from the shaft and the turbinewheel, is provided preferably with two waisted portions which result ingood flexibility of the shaft. The thermal expansion of the componentsin the shaft assembly can also be compensated, which allows plasticizingand therefore imbalance variation to be avoided.

The compressor wheel can nevertheless still be centered in the bestpossible fashion, as far as over the support regions, at its points withthe least bore flaring.

Further details, advantages and features of the invention will emergefrom the following description of exemplary embodiments on the basis ofthe appended drawing, in which:

FIG. 1 shows a perspective sectional view of an exhaust-gas turbochargeraccording to the invention,

FIG. 2 shows a side view of a shaft assembly according to the invention,

FIG. 3A shows a perspective illustration of a shaft nut of the shaftassembly according to the invention,

FIG. 3B shows a sectional illustration of the shaft nut according toFIG. 3A,

FIG. 4 shows a side view of a compressor wheel of the shaft assemblyaccording to the invention,

FIG. 5 shows a sectional illustration of a sealing sleeve of the shaftassembly according to the invention, and

FIG. 6 shows a side view of a rotor of the shaft assembly according tothe invention.

The perspective sectional view of FIG. 1 shows an exhaust-gasturbocharger 1 which has a turbine housing 39, a bearing housing 4 and acompressor housing 10 with a compressor spiral 13.

Arranged in the interior of the bearing housing 4 is a shaft 5, to theturbine-side end of which is fastened a turbine wheel 2 and to theopposite end of which is fastened a compressor wheel 12 in a housinginterior space 11 of the compressor housing 10. The shaft 5, which withthe turbine wheel 2 and compressor wheel 12 fastened thereto forms arotor of the exhaust-gas turbocharger, is supported in the bearinghousing 4 by means of two floating sleeve bearings 6, 7 which aresupplied with lubricant via two oil supply lines 8, 9 formed in thebearing housing 4.

FIG. 2 shows a side view of a shaft assembly 1A according to theinvention of the exhaust-gas turbocharger 1 with the turbine wheel 2fastened to the turbine-side end of the shaft 5 and with the compressorwheel 12 fastened to the other end of the shaft 5. Here, to fasten thecompressor wheel 12, a stop disk 37, a sealing sleeve 14 and thecompressor wheel 12 are pushed onto or attached to the free end region16 of the shaft 5 as far as its region 38 which has a greater diameterthan the free end region 16 of the shaft 5. The compressor wheel 12, thesealing sleeve 14 and the stop disk 37 are fixed to the rotor by meansof a shaft nut 15. Here, waisted portions 33, 34 and support regions 35,36 (see FIG. 5) are also provided on the end region 16 of the shaft 5.

As can be seen from the perspective illustration of FIG. 3A, the shaftnut 15 has, on a first housing region 24, an end-side contact surface 21which faces toward the compressor wheel 12. On account of the largecontact surface 21, a reduced contact pressure or greater preload forceis obtained between the shaft nut and the compressor wheel 12. As can beseen from the sectional illustration of FIG. 3B, the shaft nut 15 has aportion 19 which is divided into the first region 24 with a diameter D₃and a second region 22 with a diameter D₄. The region 22 is adjoined bya third region 23 with a diameter D₅. Here, the diameter D₃ is greaterthan the diameter D₄, which in turn is greater than the diameter D₅. Inthe portion 19 adjoining the compressor wheel 12, the shaft nut 15 has aturned recess 18 which adjoins the internal thread 17 and which has aninner diameter D₂ greater than the internal thread diameter D₁, whichinner diameter D₂ extends in the first region. 24 as far as partiallyinto the second region. 22. In contrast, the internal thread 17 extendsin the third region 23 as far as partially into the second region 22.The turned recess 18 in the shaft nut 15 results in a shortenedengagement length of the internal thread 17 into the external thread 5,and therefore an increase in the expansion length of the shaft nut 15.

The perspective illustration of FIG. 4 shows a compressor wheel 12 whosestructural length is formed by means of a shortening of the hub inrelation to conventional compressor wheels. Here, the plane of the startof the hub projects axially beyond, the plane of the blade leading edgesapproximately only by the distance of the blade root rounding. The shortstructural length of the compressor wheel 12 leads to a smaller lengthexpansion of the component in the event of heating. In order to furtherreduce the stress in the shaft assembly, the compressor wheel 12 of theshaft assembly according to the invention is preferably produced from analuminum alloy on account of its having a coefficient of thermalexpansion twice that of steel.

As can be seen in detail from the sectional illustration of the sealingsleeve 14 in FIG. 5, the sealing sleeve 14 has a sleeve housing 25 witha passage recess 26. The passage recess 26 has two end regions 27, 28whose inner diameters D₆, D₇ are greater than an inner diameter D₈ of acentral region 29, which is arranged between the end regions 27, 28, ofthe passage recess 26. Here, a length L₃ of the central region 29 of thesealing sleeve 14 is preferably greater than the lengths L₁, L₂ of theend regions 27, 28, which in turn are preferably identical. As can alsobe seen from FIG. 5, in each case one transition region 30 and 31 whichincreases continuously in diameter is provided between the end regions27 and 28 and the central region 29.. On account of the inner diametersD₆ and D₇ which are enlarged in relation to the central region 29 byturned recesses, the sealing sleeve 14 can tilt about its center ofgravity on the shaft 5 and thereby rest evenly and without bendingstresses on both sides.

The side view from FIG. 6 shows a rotor of the shaft assembly IAaccording to the invention. As can be seen from FIG. 6, the shaft 5 herehas, as viewed from the direction of the turbine wheel 2, the shaftregion 38 with a continuously constant diameter, which shaft region 38is adjoined by a bearing region 32 for the compressor wheel 12. Thebearing region 32 has two waisted portions 33 and 34 with an outerdiameter A₁ and A₂ respectively and has two support regions 35 and 36with an outer diameter A₃ and A₄ respectively, which support regions 35and 36 adjoin or are arranged adjacent to the waisted portions 33, 34.Here, the compressor wheel 12 is centered on the support regions 35 and36, while the waisted portions 33 and 34 considerably increase theelasticity and the thermal expansion or flexibility of the shaft 5, as aresult of which the thermal expansion of the components in the shaftassembly is better compensated.

To supplement the disclosure, in addition to the above writtendisclosure of the invention, reference is hereby explicitly made to thediagrammatic illustration thereof in FIGS. 1 to 6.

List of Reference Symbols

1 Exhaust-gas Turbocharger

1A Shaft Assembly

2 Turbine wheel

3 Compressor

4 Bearing Housing

5 Shaft

6, 7 Floating Sleeve Bearing

8, 9 Oil Supply Lines

10 Compressor Housing

11 Housing Interior Space

12 Compressor Wheel

13 Compressor Spiral

14 Sealing Sleeve

15 Shaft Nut

16 Free End Region of the Shaft

17 Internal Thread

18 Turned Recess

19 Portion

20 Transition Region

21 Contact Surface

22, 23, 24 Regions

25 Sleeve Housing

26 Passage Recess

27, 28 End Regions of the Passage Recess

29 Central Region

30, 31 Transition Regions

32 Bearing Region

33, 34 Waisted Portions

35, 36 Support Regions

37 Stop Disk

38 Shaft Region

39 Turbine Housing

40 Plane of Start of Hub

41 Blade Leading Edge Plane

R Blade Root Rounding

1. A shaft assembly (1A) of an exhaust-gas turbocharger (1) having a shaft (5), having a turbine wheel (2) connected to one end of the shaft (5) to form a rotor, having a compressor wheel (12) connected to the other end of the shaft (5), having a sealing sleeve (14) located on the shaft (5) on that side of the compressor wheel (12) which faces toward the turbine wheel (2), having a shaft nut (15) screwed by means of an internal thread (17) onto a free end region (16) of the shaft (5) to fix the compressor wheel (12), wherein the shaft nut (15), in a portion (19) adjacent to the compressor wheel (12), has a turned recess (18) which adjoins the internal thread (17) and which has an inner diameter (D2) greater than the internal thread diameter (D1).
 2. The shaft assembly (1A) as claimed in claim 1, wherein the turned recess (18) adjoins the internal thread (17) via a transition region (20) with a continuously increasing diameter.
 3. The shaft assembly (1A) as claimed in claim 1, wherein, that portion (19) of the shaft nut (15) which is adjacent to the compressor wheel (12) has a region (24) with a contact surface (21) whose outer diameter (D3) is greater than the outer diameters (D4, D5) of adjoining regions (22, 23).
 4. The shaft assembly (1A) as claimed in claim 1, wherein the sealing sleeve (14) has a sleeve housing (25) with a passage recess (26) which has two end regions (27, 28) whose inner diameters (D6, D7) are greater than an inner diameter (D8) of a central region (29) arranged between the end regions (27, 28).
 5. The shaft assembly (1A) as claimed in claim 4, wherein the lengths (L1, L2) of the end regions (27, 28) are equal.
 6. The shaft assembly (1A) as claimed in claim 5, wherein the length (L3) of the central region (29) is greater than the lengths (L1, L2) of the end regions (27, 28).
 7. The shaft assembly (1A) as claimed in claim 4, wherein in each case one transition region (30 and 31) with a continuously increasing diameter is provided between the end regions (27, 28) and the central region (29).
 8. The shaft assembly (1A) as claimed in claim 1, wherein the shaft (5) has a bearing region (32), which extends from the free end region (16) in the direction of the turbine wheel (2), for the compressor wheel (12), which bearing region (32) comprises two waisted portions (33, 34) whose outer diameters (Al and A2) are smaller than the outer diameters (A3 and A4) of support regions (35, 36) adjoining the waisted portions (33, 34).
 9. The shaft assembly (1A) as claimed in claim 1, wherein the compressor wheel (12) is composed of an aluminum alloy.
 10. The shaft assembly (1A) as claimed in claim 1, wherein a stop disk (37) is arranged between the sealing sleeve (14) and a shaft region (38) of the shaft (5).
 11. The shaft assembly (1A) as claimed in claim 1, wherein the plane of the start of the hub (41) of the compressor wheel (12) is situated remote from the blade leading edge plane (40) approximately by the distance of the blade root rounding (R). 